Production of refractory conductors.



UNITED: STATES r CrENT oFFIcE.

WILLIAM B. oooLnJGn, or scn'nnnc'ranr, NEW YORK, ASSIGNOR 'ro ennnnar.

. nnncrnrc comranr, A conronarron on NEW YORK.

No Drawing.

. PRODTIGTION; OF REFRACTORY CONDUCTORS.

Patented Nov. 4, 19 13.

To-allwhom it may concern:

Be it known thatI, WILLIAM D. COOLIDGE, a citizen of the United States, residing at Schenectady, in the county of Schenectady, State of New York, have invented certam new and useful Improvements in the Production of Refractory Conductors, of which the following is a specification.-

This invention relates tothe production of refractory electrical conductors suitable .foruse in incandescent lamps, electric furnaces, and other apparatus, and comprises a process whereby refractor material, even though non-ductile, may shaped into wires, plates, rods, tubes, or other forms, and thentreated to produce coherent c0n-.

' ductors capable of converting electrical, en-

' erg'y into heat and light at enormously high temperatures.

" According to my present invention, arefractory element, alloy, compound or mixture is incorporated in a metallic binder, and the product so obtained is'squirted or otherwise' shaped into rods, filaments,-or the like, and then treated to dry it'out, that is, to

bring it to sucha state that subsequent heating will not make it soft; after which the rods or filaments are still further treated to free them from all easily vaporizable components and to. sinter together the refractory residueinto a coherentconductor.

' with refractory powder and capa As, a binding'material I may use various cadmium alloys capablegof 1m regnation his of sub- .sequent extrusion through a die without I separation of some component ofthe mix- 'ture, and, finally, capable of. removal from the refractory powder to leave behind a coherent conductor free 1 from easily vaporizable material. As such an alloy, I may use one containing cadmium, mercury, and hismuth. This alloy may have the following p'roportions,cadmium 44%, mercury and bismuth 12%. This binder does not ap-' pear to chemically combine with the refractory. material with which it is impregnated, an consequently, the process of manufacture is'applicable to all the materials above mentioned and to many others .In general, the binding material serves to give'the mixture plasticity and strength,

andin some cases to increase its'electrical conductivity, and is retained in the mixture only until the body has been worked or formed into the desired shape. It is then I taken out by'suitable treatment and leaves behind a refractory coherent wire, rod, tube,

" or the like. 4 In order that my invention may be easily practised, I have hereinafter described the processas applied to the metal tungsten, and as applied toa metal binder of cadmiumbismuth-amalgam, but this specific embodiment is to be regarded as only typical and as showing but one of numerous ways of utilizing myinvention.

ungsten suitable for use according to my present process may be made by reduction of tungsten trioxid-with hydrogen according to the general process well-known to chemists, except, however, that the reaction should preferably be so conducted that the resulting tungsten is in a very finely divided condition. To obtain this result, I find it desirable to use very fine tungsten trioxidand to treat this oxid at a relatively high temperature using a large quantity of hydrogen. To compound the binder for use with tungsten or other refractory powder, I melt together the bismuth, cadmium and mercury 'in the proportions above mentioned. I find that the mixture melts considerably lower than'the temperature at which cadmium oxidizes in air, and I find that th'e'alloy is smooth, and when partially cooled is plastlc .'and' maybe readily impregnated with tungsten powder by simply rubbing the two together with a 'pestlein a chemists mortar. The tungsten may be added to the extent of'30 to 40% by weight of the final mixture. I call the product a mixture because I"do-not.

atppresent believe that the tungsten alloys.

01; combines in any Way with the material of the binder, The mixture is tenacious and pliable'and can be readily rolled or worked by well-known metal-working processes;

1 To obtain wires suitable for the construction of incandescent lam-p filaments, I squirt the plastic composite mixture above men tioned through adiamond die at a temperature of'lOO ire-150 degreesgC. -The material comes out asa smooth silver white wire, very strong, pliable and tough. It can be vsquirted 'invsizes varying from large rods down to wires having a diameter of one mil -"or even less. Aftercutting these ductile. wiresto proper length and bending into ,loops-havingthe shape of lamp filaments they-are treated to dry out the binder and .to

put the conductors in such condition that they will not become unduly soft when heated above the liquefying-temperature of the remaining binding agent. To effect this drying operation I may follow any one of the several methods hereinafter described, each of which has some advantages,

. According to 'oneimethod of procedure the, filament-shaped loops are placed in bundles.

on a piece of wire gauzesupported in a-rel'a tively small glass-tube heated externally, as by a gas flame, and are there subjected to a current or blast of hydrogen or 'other gaseous or vaporous fluid capable of drying-out and carrying away some of ,the warm binder. It is'mypresent opinion that during this drying operation some, or possibly all, of the mercury 'sublimes orevaporates and is taken up by the. blast- 0f hydrogen-or other fluid andso carriedaway before ithas' formed large globules which might pit the surface of the Wires by amalgamation or alloying with the binder immediately adjacent.

If hydrogen-is used 'as the" drying agent,-

I prefer not to let it go to waste after once passing the filaments, but instead, I return it to the tube over and over again, as by means of a suitable circulating pum The pressure of the'hyd-rogen in the tu e may vary an where from atmospheric to almost zero an apparently, the faster it circulates, the more rapidly is the mercury or similar component removed from the Wires under treatment.

'I have suggested-hydrogen as the gaseous material for the blast, but nitrogen is also suitable, or a mixture of nitrogen and hydro- Of course, themercury vapor ought' not tobe disc-liar ed into the room where the 'opera-tors are at work, as it is injurious to health.

' When air or'steam is used asthe drying agent, a second action comes into play bc' cause of the chemical reaction between the drying fluid and thewires under treatment.

Air or steam will tend to' oxidize the cad- .mlum -somewhat, but, this oxidation, in-

stead of being harmfuhis in truth helpful, sincethe formation of cadmium oxid means the removal of a liquid element from the wire and the production in its place of a dry powder, namely, cadmium oxid, which still further dries out .the wire.- Even in case the treatment with fluid is carried so far as to oxidize some of the tungsten, no trouble need arise therefrom'if the filaments are subsequently sintered in hydrogen, as by means of external heat. As hereinafter described, this procedure reduces the tungsten oxid to metal, and the resulting product is the same as'it' no oxidation had occurred".

If desired, the heatnecessary for most advantageousoperation of the process may be applied, not only to the tube containing the wires, but also to the circulating fluid before it enters the baking or drying tube.

In case air or steam is used as the drying fluid, it need not be circulated so rapidly as in the case of the inert hydrogen or nitrogen. This is due, ojf course, to thefact that thevapo'rizing action of the air or steam is supplemented by their chemical action on the wires. vThough I consider it best to supply the air or steam as a blastor'circulating current,--the speed of circulation can profitably be rgulated'to' suit the particular tem .peratureoftreatment and the chemical activity of the treating fluid with respect to the particular metals under treatment.

By the substitution of other fluids for the air or steam, it is possible to dispense entirely with the circulating features and to depend solely on the chemical action of the treating fluid. Thus, if the wires be subjected to the action of acid fumes, they can be dried out sufficiently forthepurpose at hand, even though the fumes be not circulated over the wires to any appreciable extent. As suitable gaseous re-agents for this work I may use hydrochloric acid, chlorin, bromin, hydrogen sulfid or ozone either at atmospheric pressure or at reduced pressure and I may continue the treatment with the re-agent until the wires are dried out to the desired extent, namely, to such a degree as to permit the necessary high heat treatment without softening. It is my present understanding that the action produced by these gaseous re-age'nts consists in the formation of solid compounds'in the warm or heated wires in place of the metals which might otherwise ooze out on the surface and form flaws or pits by alloying with the meta-l binder immediately adjacent. Some of these re agcnts may be used at room temperature, in w ich case supplemental heating is not necessary. F r a It may be understood that wires treated by the above enumerated chemical re-agents no longer consist solely of metal, but contain also other elements or compounds. Consequently,"subsequent steps of the treatment should be carried out with the view to decompounds. i v

proceed by the wires in sa packing of nos-men the untreated wire .is a porous net-work of tungsten filled with binder, and that, on heating to the softening point, capillary forces push out large quantities of the liquefied binder with the production of large globules at the surface of the wire. The useof a packing of finely divided metal capable of uniting readily with the exuded mercury prevents formation ofthese globules and permits carrying the filaments through that somewhat delicate stage wherein they tend to soften to a troublesome extent as the temperature is raised. With that portion of the binder which would otherwise tend to form globules removed, there is no apparent need for further preliminary baking or drying and the wires can immediately be subjected to the final or finishing treatment, though, if? desired, the drying or baking process can be carried further, and more of the binder removed by alloying with the metal packing or by direct volatilizat-ion. The metal packing can be brushed from the filaments or wires after the drying treatinent, and what little remains sticking to them can be volatilized off in the subsequent firing operation. The packing of finely divided metal. serves so completely to protect the wires that-it is even possible to bake them in open boats heated in air.

As a still further modification of the drying or baking operation, I may pack the Wires in very finely divided inert powders,

such as alumina, magnesia, calciumcarbo-' nate, cupric oxid, silica, tungsten, carbon, or manganese-dioxid. The inert powder should be exceedingly fine and should be well shaken about the wires so that every bit of the surface of the wires is covered with the packing material. Baking may then take place as usual, either in a vacuum or a gaseous atmosphere, such as hydrogen. The very finely divided packing seems in some way to prevent the formation of harmful globules, even in a quiet gas at atmospheric pressure. The baking operation may be stopped at any time after removal of such proportion of the components of the metal binder as would otherwise rendea the wires too wet for the direct application of high temperature treatment. During this drying or bakmg operation, whether carried out.by the use of a strong blast of inert. gas, or by. a' chemlcal re-agent either quiescent or circulatin or by heating in fine powder, either inert or chemically active, so, much of the through the finishingt mercury and cadmium should be taken out of the wires, or replaced by oxid or other compound, that the wires can then be put high heat treatment without danger of so ehing up to a troublesome extent because of liquefaction of the binder.

The final or firing treatment may be carried out in one of several ways, as, for instance, by heating with current in a vacuum or in an atmosphere of hydrogen or hydrogen and nitrogen, containing the heat treatment until all easily vaporizable components are removed from the wire and until the re- -mg the filaments with heat from an external source, as by heating in a tubular resistance furnace operated at high temperature, and, if necessary, supplied with an inert or chemically active gas. The use of such a furnace is particularly advantageous in case the bakingv or drying treatment has left in the wires some oxid, chlorid,or other compound, requiring the use of a reducing agent for its convenient removal.

While my invention is described with particular reference to the manufacture of tungsten filaments, I have found by investigation and therefore wish it to be understood that it is of generalapplication to other refractory metals and materials, such, for example, as molybdenum, graphite, or the like.

Having now fully described my invention, what I claim as new and desire to secure by Letters Patent of the United States, is:

1. The method which consists in heating a molded article comprisin a refractory powder and a metal binder in the presence of means for progressively taking up at least-some of the more easily fusible portion of said binder to stiffen the article and prevent its undue softening when heated to a higher temperature;

2. The method of preparing an unfinished lamp filament comprising refractory material and an amalgam binder for hi h heat treatment which consists in heating 1; e same '1'n a stream of fluid to remove part of the binder, and regulating the rate of fiow of. said fluid to prevent the formation of surface globules.

3. The method which consists in heatin articles comprising refractory material an an amalgam binder in a strong current of gas to progressively remove some of the metal binder and finally heating by heat generated externally to a-higher tem erature to com lete the removal of the binder and consoli ate the residue.

4. In the process of'making tungsten fila- 10 in the presence of means-for removing excase in the Patent Oflice.

[SEAL] Correction in Letters Patent No, 1,077,674. H

my hand this 21st day of September 1908.

'uded metal from the surface at a rate which will prevent large globules from forming on the surface of said body.

In witness whereof, I have hereunto set WILLIAM D. COOLIDGE.

Witnesses:

BENJAMIN B. HULL, MARGARET E. WOOLLEY.

It is hereby certified that in Letters Patent No. 1 ,O77,674, grantedNovember I 4, 1913, upon the application of William D. Coolidge, of Schenectady, New York, for an improvement in the Production of Refractory Conductors, an error appears in the printed specification requiring correction as follows: Page 3, line 76, for the word containing read co nta'nuz 'ngj'and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the Signed and sealed this9th day of December, A. D., 1913.

J. T. NEWTON,

Acting Commissioner of Patents. 

